Thermoplastic saturated norbornene based resin film, and method for producing thermoplastic saturated norbornene based resin film

ABSTRACT

It is an object of the invention to provide a thermoplastic saturated norbornene resin film, an optical film, a protective film for a polarizer, a retardation film, a polarizing plate obtainable by this, which realizes the compatibility between excellent physical properties and optical characteristics, and a method of producing a thermoplastic saturated norbornene resin film. The invention relates to a thermoplastic saturated norbornene resin film, which is obtainable by using a thermoplastic saturated norbornene resin composition containing a thermoplastic saturated norbornene resin in an amount of 100 parts by weight and a rubber polymer in an amount of 5 to 40 parts by weight, parallel transmittance being 87% or more.

FIELD OF THE INVENTION

The present invention relates to a thermoplastic saturated norborneneresin film, an optical film, a protective film for a polarizer, aretardation film, a polarizing plate, which realizes the compatibilitybetween excellent physical properties and optical characteristics, and amethod of producing a thermoplastic saturated norbornene resin film.

BACKGROUND ART

Thermoplastic saturated norbornene resins have excellent performances inheat resistance, optical characteristics, transparency, electriccharacteristics and the like and their applications as films used forparts for automobiles, electric and electronic parts, optical componentsand construction materials are considered. Among others, there areexpected applications as a protective film for a polarizer or aretardation film, which is used in liquid crystal displays of desktopelectronic calculators, electronic watches, word processors, instrumentsof automobiles and machineries, and the like.

The polarizing plate generally comprises a polarizer obtainable byallowing a polyvinyl alcohol resin oriented by drawing to adsorb iodineor dye with dichroism and protective films for a polarizer bonded toboth sides of the polarizer. It is required for an optical film to beused as a protective film for a polarizer to be superior in opticalcharacteristics such as optical transparency and to have a mechanicalstrength capable of preventing the shrinkage of a polarizer having largeshrinkage and heat resistance capable of resisting high temperaturessubjected in a manufacturing process.

Conventionally, as the protective film for a polarizer, optical filmscomprising triacetyl cellulose have been used. However, the optical filmcomprising triacetyl cellulose had problems that it had excellentoptical characteristics but was insufficient in heat resistance andmoisture resistance, and when it was used for a long time in an hot orhumid atmosphere, a significant reduction in a degree of polarization,peeling between a polarizer and a protective film and deterioration oftransparency due to hydrolysis of triacetyl cellulose had occurred andperformance of the polarizing plate had been deteriorated.

And, in the polarizing plate, a retardation film is used for the purposeof compensating a strain of light in passing through a liquid crystalmaterial. As such a retardation film, there has been used a substancecomprising resin which is superior in transparency and heat resistancesuch as a polycarbonate resin or a polysulfone resin.

In Japanese Kokai Publication Hei-5-247324, there is disclosed anoptical film comprising a thermoplastic saturated norbornene resin. Theoptical film comprising the thermoplastic saturated norbornene resinexhibits a feature that development of birefringence corresponding to astress is small, excellent optical characteristics such as hightransparency and in addition excellent heat resistance. Accordingly, ifthe optical film comprising a thermoplastic saturated norbornene resinis used, it can be expected to obtain a polarizing plate havingexcellent optical characteristics.

However, the optical film comprising a thermoplastic saturatednorbornene resin had a problem that it was very brittle and productionof a thin film was difficult. And, even when the production of theoptical film by an extrusion process was tried, since a film broke inthe case where a take off speed was high, there was also a problem inproductivity.

In manufacturing of liquid crystal displays, there is conducted a stepof bonding a polarizing plate to a liquid crystal cell, but it cannot beavoided that bubbles or contamination is involved in bonding and thatthere are defects in the polarizing plate itself. Therefore, there isconducted a step referred to as a rework, in which an inspection iscarried out after the step of bonding a polarizing plate to a liquidcrystal cell, and when defects are present, the polarizing plate ispeeled to reuse the expensive liquid crystal cell. In order to enablesuch a reuse, it was necessary that the polarizing plate might be easilyremoved in peeling it, but in the case of a polarizing plate using aprotective film for a polarizer or a retardation film, comprising abrittle thermoplastic saturated norbornene resin, there was a problemthat the polarizing plate might break in peeling it and reworkabilitywas poor.

Correspondingly, in Japanese Kokai Publication Hei-3-106963, there isdisclosed a resin composition containing a hydrogenated ring-openingnorbornene polymer and rubber. It is described that this is a resincomposition, which can provide a molded article inhibiting crack or sinkduring molding when using it for insert molding of metal parts by addingrubber to a hydrogenated ring-opening norbornene polymer. It isconsidered that physical properties of this resin composition such asbrittleness of a norbornene resin are improved. However, opticalcharacteristics such as parallel transmittance were significantlydeteriorated due to addition of rubber and therefore it could not beused as an optical film.

In Japanese Kokai Publication Hei-5-247324, there is also described athermoplastic saturated norbornene resin composition, which comprises athermoplastic saturated norbornene resin and a compounding agent beingnot compatible with it and in which the compounding agent is dispersedforming micro domains, and optical materials obtainable by this. And, itis disclosed that when a rubber polymer is used as a compounding agent,adhesion to various coating materials or films can be improved. However,an amount of rubber polymer to be added was specified to be about 0.001to 0.8 parts by weight per 100 parts by weight of the thermoplasticsaturated norbornene resin to attain sufficient optical performance, andaddition of the compounding agent of this extent could not realize asufficient improvement in physical properties.

And, in Japanese Patent Publication No. 2940014, there is disclosed athermoplastic resin composition comprising a thermoplastic saturatednorbornene resin and a rubber polymer. Also, there is described a moldedarticle obtainable by injecting the thermoplastic resin composition.However, in Japanese Patent Publication No. 2940014, impact resistanceand total transmittance of the obtained molded article were describedbut production of optical films was not described at all, and paralleltransmittance and haze, which were essential to performance of anoptical film, were not described at all, either.

Further, in Japanese Kokai Publication Hei-5-148413, there is discloseda film obtainable by dissolving or dispersing a thermoplastic saturatednorbornene resin and a rubber component in a solvent and molding them bya casting method. It is described that elongation is improved byblending a rubber component into a thermoplastic saturated norborneneresin. However, the obtained film was poor at optical characteristicssuch as parallel transmittance and could not be used as an optical film.

SUMMARY OF THE INVENTION

In view of the state of the art, it is an object of the presentinvention to provide a thermoplastic saturated norbornene resin film, anoptical film, a protective film for a polarizer, a retardation film, apolarizing plate and a method of producing a thermoplastic saturatednorbornene resin film, which realize the compatibility between excellentphysical properties and excellent optical characteristics.

The first aspect in the present invention pertains to a thermoplasticsaturated norbornene resin film which is obtainable by using athermoplastic saturated norbornene resin composition containing athermoplastic saturated norbornene resin in an amount of 100 parts byweight and a rubber polymer in an amount of 5 to 40 parts by weight,parallel transmittance being 87% or more.

Preferably, the difference of refractive indexes between thethermoplastic saturated norbornene resin and the rubber polymer is 0.2or less.

Preferably, the thermoplastic saturated norbornene resin film of thefirst aspect in the present invention has a tensile elastic modulus of900 MPa or higher and a tensile elongation at break of 4 to 40%, and hasresidual retardation of 3 nm or lower and displacement of the opticalaxis of ±10° or smaller with respect to a machine direction, and morepreferably, it has the residual retardation of 1 nm or lower. And, it ispreferred that the difference between the maximum thickness and theminimum thickness in measuring a film thickness by a method according toJIS K 7130 is 5 μm or smaller and it may be rewinded without breakingwith tension of 500 N/650 mm.

The rubber polymer is preferably a styrenic elastomer and the styrenicelastomer is preferably a styrene-ethylene-butylene copolymer, thecontent of a styrene component being 25 to 50% by weight and the contentof an ethylene component being 25 to 50% by weight.

Preferably, the thermoplastic saturated norbornene resin compositionfurther contains a thermoplastic resin having a number average molecularweight of 300 to 10,000.

Preferably, the thermoplastic saturated norbornene resin film of thefirst aspect in the present invention has a photoelastic coefficient of2.0×10⁻¹¹ Pa⁻¹ or smaller.

An optical film, a protective film for a polarizer and aretardation filmcomprising the thermoplastic saturated norbornene resin film of thefirst aspect in the present invention also constitute the presentinvention.

The second aspect in the present invention pertains to a polarizingplate, which comprises a protective film for a polarizer, comprising anorbornene resin composition, and a polarizer parallel transmittancebeing 40% or more and not breaking in peeling off the polarizing platewith a tensile speed of 300 mm/min and tension of from 2.5 to 3 N/25 mmunder the conditions of a 180 degree peel test according to JIS Z 1528.

In the polarizing plate of the second aspect in the present invention,it is preferred that the rate of change in dimensions measured beforeand after heating at 90° C. for 24 hours is 2% or less.

A polarizing plate, which is obtainable by laminating the retardationfilm of the present invention directly on at least one side of thepolarizer, also constitutes the present invention.

A method of producing the thermoplastic saturated norbornene resin filmof the first aspect in the present invention by a melt extrusionprocess, wherein a melting temperature of the thermoplastic saturatednorbornene resin composition during melting the thermoplastic saturatednorbornene resin composition and sending the thermoplastic saturatednorbornene resin composition to a die is a glass transition temperatureof the thermoplastic saturated norbornene resin plus 135° C. or lowerand an average residence time from melting the thermoplastic saturatednorbornene resin composition to sending it to a die is 40 minutes orless, also constitutes the present invention.

In the method of producing a thermoplastic saturated norbornene resinfilm of the present invention, temperature, immediately prior to contactwith the chill roll, of the thermoplastic saturated norbornene resincomposition extruded from a die is preferably a glass transitiontemperature of the thermoplastic saturated norbornene resin plus 50° C.or more, and it is more preferably a glass transition temperature of thethermoplastic saturated norbornene resin plus 80° C. or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of a transmission electronmicrograph of a cross section of a thermoplastic saturated norborneneresin film of the first aspect in the present invention.

FIG. 2 is a schematic view showing an example of a transmission electronmicrograph of a cross section of a conventional thermoplastic saturatednorbornene resin film.

FIG. 3 is a transmission electron micrograph of a cross section of athermoplastic saturated norbornene resin film prepared in Example 1.

In these drawings, a reference numeral 1 represents a thermoplasticsaturated norbornene resin and a reference numeral 2 represents a rubberpolymer.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail.

A thermoplastic saturated norbornene resin film (hereinafter, alsoreferred to as a TPSNB resin film) of the first aspect in the presentinvention is a film obtainable by using a thermoplastic saturatednorbornene resin composition (hereinafter, also referred to as a TPSNBresin composition) containing a thermoplastic saturated norbornene resin(hereinafter, also referred to as TPSNB resin) and a rubber polymer.

In the present description, a TPSNB resin refers to a polymer of anorbornene monomer or a copolymer of a norbornene monomer and a monomerwhich can copolymerize with it, not having an unsaturated bond in amolecule, or hydrogenated to an unsaturated bond in the case of havingan unsaturated bond in a molecule.

The norbornene polymer is not particularly limited but for example, asubstance obtainable by polymerizing at least one species of norbornenemonomers expressed by the following general formula (1) or a substanceobtainable by copolymerizing at least one species of norbornene monomersexpressed by the following general formula (1) and a copolymerizablemonomer which may copolymerize with this are suitably used.

In the formula (1), wherein A and B are independent of each other andrepresent a hydrogen atom or a hydrocarbon group having 1 to 10 carbonatoms, X and Y are independent of each other and represent a hydrogenatom, a halogen atom or an organic group, and m is an integers of 0 to1.

The norbornene monomer expressed by general formula (1) is notparticularly limited but it is suitably, for example, a substance nothaving a functional group such as bicyclo[2.2.1]-2-heptene,tricyclo[5.2.1.0^(2,6)]-8-decene, tricyclo[5.2.1.0^(2,6)]-3-decene,tricyclo[6.2.1.0^(1,9)]-9-undecene, tricyclo[6.2.1.0^(1,9)]-4-undeceneand tetracyclo[4.4.0.1^(2,5)1^(7,10)]-3-dodecene; and a substance havinga functional group such as8-methoxycarbonyltetracyclo[4.4.0.1^(2.5).1^(7,10)]-3-dodecene,8-methyl-8-methoxycarbonyltetracyclo[4.4.0.1^(2,5).1^(7,10)]-3-dodeceneand 5-methoxycarbonyl-bicyclo[2.2.1]-2-heptene are suitable. Amongothers, tetracyclododecene derivatives, in which m is 1 in the generalformula (1), is suitable in that a polymer having a high glasstransition temperature can be obtained. These norbornene monomers may beused alone or in combination of two or more species.

A copolymerizable monomer which can copolymerize with the norbornenemonomer expressed by the general formula (1) is not particularly limitedand includes, for example, norbornene monomers not contained in thegeneral formula (1) and cyclic olefinic monomers not having a norborneneskeleton. As a norbornene monomers not contained in the general formula(1), there are given polycycloalkene such aspentacyclo[6.5.1.1^(3,6).0^(2,7).0^(9,13)]-4-pentadecene, pentacyclo[6.6.1.1^(3,6).0^(2,7).0^(9,14)]-4-hexadecene,pentacyclo[6.5.1.1^(3,6).0^(2,7).0^(9,13)]-11-pentadecene,dicyclopentadiene andpentacyclo[6.5.1.1^(3,6).0^(2,7).0^(9,13)]-pentadeca-4,11-diene.

The cyclic olefinic monomers not having a norbornene skeleton is notparticularly limited and includes for example, cycloolefines such ascyclopentene, cyclooctene, 1,5-cyclooctadiene and1,5,9-cyclododecatriene.

A method of polymerizing a norbornene monomer expressed by the generalformula (1) or a method of copolymerizing a norbornene monomer expressedby the general formula (1) and a copolymerizable monomer which maycopolymerize with this is not particularly limited and for example, aconventional method publicly known, such as ring-opening metathesispolymerization, addition polymerization may be employed.

A method of hydrogenating the norbornene polymer or the norbornenecopolymer is not particularly limited and includes, for example, amethod of using a publicly known catalyst such as Wilkinson complex,cobalt acetate/triethylaluminum, nickelacetylacetonato/triisobutylaluminum, palladium-carbon, rutheniumcomplex, ruthenium-carbon and nickel-diatomite. When metathesispolymerizable complexes, such as ruthenium-alkylidene complex,ruthenium-vinylidene complex, and ruthenium-Fischer carbene complex, isused in polymerizing, hydrogenation can be performed by pressurizingwith hydrogen without adding a catalyst for hydrogenation and thereforea polymerization step and a hydrogenation step can be performedsequentially.

The hydrogenation is generally performed at 0 to 250° C. under ahydrogen pressure of 1 to 200 atmospheres in a homogeneous system or aheterogeneous system depending on kinds of catalyst.

The TPSNB resin means a substance to which hydrogen is added in such away that a hydrogen addition ratio is at least 50% or higher in the casewhere the norbornene polymer or the norbornene copolymer has theunsaturated bond in a molecule but a hydrogen addition ratio ispreferably 90% or higher and more preferably 99% or higher. When thehydrogen addition ratio is lower than 50%, light resistance and heatresistance of the TPSNB resin film of the first aspect in the presentinvention to be obtained are poor.

A number average molecular weight, on the polystyrene equivalent basis,of the TPSNB resin is preferably 10,000 to 1,000,000. When it is lessthan 10,000, the mechanical strength of the resulting TPSNB resin filmof the first aspect in the present invention may be insufficient, andwhen it is more than 1,000,000, the ability to be melt-molded may besignificantly reduced. It is more preferably 15,000 to 700,000.

In addition, since a desired effect is easy to attain even when anamount of a rubber polymer to be blended is decreased, it is preferredthat a TPSNB resin having a higher molecular weight is used within thelimits of satisfying another requirements such as the ability to bemelt-molded.

A glass transition temperature of the TPSNB resin is preferably 70 to180° C. When it is lower than 70° C., heat resistance of a TPSNB resinfilm of the first aspect in the present invention to be obtained may bepoor, and when it is more than 180° C., molding may become difficult.

The TPSNB resin composition contains a rubber polymer.

In the present description, the rubber polymer is a polymer comprising ahard segment and a soft segment and refers to a substance in which aglass transition temperature of the soft segment is 25° C. or lower.

The rubber polymer is not particularly limited and includes, forexample, styrenic elastomers such as styrene-butadiene block copolymer,hydrogenated styrene-butadiene block copolymer, styrene-isoprene blockcopolymer, hydrogenated styrene-isoprene block copolymer,styrene-isobutylene block copolymer, and thermoplastic elastomers suchas low crystalline polybutadiene resin, ethylene-propylene elastomer,styrene-graft ethylene-propylene elastomer, thermoplastic polyesterelastomer, ethylenic ionomer resin. These rubber polymers may bemodified by a specific functional group such as an epoxy group, acarboxyl group, a hydroxyl group, an amino group, an acid anhydridegroup, an oxazoline group. Among others, styrenic elastomers aresuitable.

The styrenic elastomer is not particularly limited as long as it canimprove the physical properties such as a tensile elastic modulus and atensile elongation at break without impairing the opticalcharacteristics of the TPSNB resin film of the first aspect in thepresent invention to be obtained, and includes, for example, a copolymercomprising a styrene segment and a segment having a glass transitiontemperature of 25° C. or lower. Among others, astyrene-ethylene-butylene copolymer (SEBS) andstyrene-ethylene-propylene copolymer are preferred. Particularly, astyrene-ethylene-butylene copolymer, in which the content of a styrenecomponent is 25 to 50% by weight and the content of an ethylenecomponent is 25 to 50% by weight, is suitable since an optical film,which realizes the compatibility between extremely excellent opticalcharacteristics and physical properties, can be obtained. It isconsidered that the reason for this is that since it has the refractiveindex being very close to that of the TPSNB resin and can efficientlyimpart rubber properties to the resin and a decrease in the elasticmodulus is small, it does not impair the characteristics of the TPSNBresin.

When the styrenic elastomer is used as the rubber polymer, a numberaverage molecular weight of the styrenic elastomer is preferably 50,000to 1,000,000. When it is less than 50,000, the dispersibility into thenorbornene resin becomes insufficient and it may be impossible to attainan effect of improvement in physical properties by addition of therubber polymer, and when it is more than 1,000,000, since themoldability is poor due to too high melt viscosity in being blended intothe norbornene resin, it may be impossible to obtain a homogeneous film.The number average molecular weight is more preferably 80,000 to 500,000and furthermore preferably 100,000 to 400,000.

The difference of refractive indexes between the TPSNB resin and therubber polymer is preferably 0.2 or less. When the difference is morethan 0.2, the transparency and the residual retardation of the resultingTPSNB resin film of the first aspect in the present invention may bedeteriorated or the optical strain may tend to develop. The differenceis more preferably 0.1 or less, furthermore preferably 0.05 or less andparticularly preferably 0.03 or less.

And, when the TPSNB resin composition is prepared by melting and mixing,a ratio (η rubber/η norbornene) between the viscosity (η norbornene) ofthe TPSNB resin and the viscosity (η rubber) of the rubber polymer at amolding temperature is preferably close to 1. When this viscosity ratiois close to 1, the rubber polymer can be finely dispersed in the TPSNBresin. This ratio is preferably 0.2 to 3.0 and more preferably 0.4 to2.0. When a haze value of the TPSNB resin film to be obtained is 0.5% orlower, it is preferred that particularly η rubber/η norbornene is 0.5 to1.8. And, the term viscosity refers to viscosity measured at a shearrate of 24.3 at an actual molding temperature.

The content of the rubber polymer is preferably 5 to 40 parts by weightper 100 parts by weight of the TPSNB resin composition in the TPSNBresin. When it is less than 5 parts by weight, a sufficient effect ofimproving the physical properties of the TPSNB resin film of the firstaspect in the present invention cannot be attained, and when it is morethan 40 parts by weight, the optical characteristics of the resultingTPSNB resin film of the present invention is poor. It is preferably 10to 30 parts by weight.

Preferably, the TPSNB resin composition further contains a thermoplasticresin. By containing the thermoplastic resin, the compatibility betweenthe TPSNB resin and the rubber polymer is enhanced and opticalcharacteristics of the resulting TPSNB resin film of the first aspect inthe present invention may be enhanced.

The thermoplastic resin is not particularly limited but olefinic resinsare suitable because of high compatibility with the TPSNB resin.

A number average molecular weight of the thermoplastic resin ispreferably 300 to 10,000. When it is less than 300, problems such asbleeding out may develop, and when it is more than 10,000, it may beimpossible to attain an effect of improving the compatibility. It ismore preferably 500 to 5,000 and furthermore preferably 600 to 2,000.

The difference of refractive indexes between the thermoplastic resin andthe TPSNB resin is preferably 0.2 or less. When the difference is morethan 0.2, the transparency of the resulting TPSNB resin film of thefirst aspect in the present invention may be poor. The difference ismore preferably 0.1 or less.

And, in the case where the thermoplastic resin is blended into the TPSNBresin composition by a method of melt kneading, it is preferred that atemperature, at which 2% by weight is degraded under an atmosphere ofair in thermogravimetry, is 230° C. or higher. The temperature is morepreferably 250° C. or higher and furthermore preferably 270° C. orhigher.

As a commercially available one of thermoplastic resins having such theproperties, there are given, for example, “Escorez” produced by TonexCorporation, “Clearon” produced by YASUHARA CHEMICAL Co., Ltd., and“ARKON” produced by Arakawa Chemical Industries, Ltd.

The TPSNB resin composition may contain, within the limits of notinhibiting the purpose of the present invention as required,anti-oxidants such as 2,6-di-t-butyl-4-methylphenol,2-(1-methylcyclohexyl)-4,6-dimethylphenol,2,2-methylene-bis(4-ethyl-6-t-butylphenol),tris(di-nonylphenyl)phosphite; ultraviolet absorbers such asp-t-butylphenylsalicylate, 2,2′-dihydroxy-4-methoxy-benzophenone,2-(2′-dihydroxy-4′-m-octoxyphenyl)benzotriazole; lubricants such asparaffin wax, hydrogenated oil; and antistatic agents such asstearoaditopropyldimethyl-β-hydroxydiethylammonium nitrate.

The TPSNB resin film of the first aspect in the present invention hasthe parallel transmittance of 87% or more. When the transmittance isless than 87%, it becomes difficult to use it in applications such as aprotective film for a polarizer. The transmittance is preferably 89% ormore.

Preferably, the TPSNB resin film of the first aspect in the presentinvention has a haze value of 5% or less. When the haze value is morethan 5%, in the case of using it in applications of a protective filmfor a polarizer and the like, light leakage may occur. The haze value ismore preferably 3% or less, furthermore preferably 1% or less andparticularly preferably 0.5% or less.

Preferably, the TPSNB resin film of the first aspect in the presentinvention has residual retardation of 3 nm or lower and displacement ofthe optical axis of ±10° or smaller with respect to a machine direction(MD). When the residual retardation is higher than 3 nm or thedisplacement of the optical axis is larger than ±10° with respect to amachine direction, in the case where the TPSNB resin film of the firstaspect in the present invention is used as a protective film for apolarizer, light leakage may occur. The lower residual retardation anddisplacement of the optical axis is more preferred, and when theresidual retardation is 1 nm or lower, since the magnitude of thedisplacement of the optical axis can be neglected and a step ofinspecting the displacement of the optical axis becomes unnecessary, aproduction process of producing the protective film for a polarizer andthe like can be more preferably simplified to a large extent.

Incidentally, the optical axis refers to a direction in which therefractive index of an incident light becomes largest, an axis generallyreferred to as a slow axis, and the displacement of the optical axisrefers to an angular displacement with respect to the machine directionof the optical axis. And, the machine direction is a direction of flowof extrusion in fabricating for example a film by extrusion.

In the TPSNB resin film of the first aspect in the present invention, itis preferred that a tensile elastic modulus, which is measured accordingto JIS K 7113, is 900 MPa or higher. When the tensile elastic modulus islower than 900 MPa, it may be impossible to inhibit shrinkage of apolarizer in the case where the TPSNB resin film of the first aspect inthe present invention is used as a protective film for a polarizer. Itis more preferably 1,000 MPa or higher. In addition, the higher tensileelastic modulus is more preferred and there is no particular upperlimit.

In the TPSNB resin film of the first aspect in the present invention, itis preferred that a tensile elongation at break, which is measuredaccording to JIS K 7113, is 4 to 40%. When the tensile elongation atbreak is lower than 4%, it is apt to break and therefore, in the casewhere the TPSNB resin film of the first aspect in the present inventionis used as a protective film for a polarizer, the ability of thepolarizing plate to be reworked may be poor. When it is higher than 40%,conducting a durability test, particularly a heat resistance aging test,changes in the dimension of the polarizing plate become large andchanges in the optical characteristics or peeling off from a liquidcrystal cell may be apt to occur. It is more preferably 6 to 35% andfurthermore preferably 8% or higher.

Preferably, the TPSNB resin film of the first aspect in the presentinvention can be rewinded without breaking with a tension of 500 N/650mm at room temperature. Thereby, the mass production becomes possibleand the cost can be significantly reduced.

Preferably, the TPSNB resin film of the first aspect in the presentinvention has a photoelastic coefficient of 2.0×10⁻¹¹ Pa⁻¹ or smaller.When the TPSNB resin film of the first aspect in the present inventionis used as a protective film for a polarizer, various external forces,such as a shrinkage stress of a polarizer, a stress based on strain inbonding it and a stress based on strain in incorporating it into adisplay, were exerted. Particularly, the shrinkage stress of a polarizeris large in hot and humid surroundings. The photoelastic coefficient isderived from the following equation;Photoelastic coefficient (c)=birefringence (Δn)/stress (σ),and is a value representing a change in birefringence by externalforces.

That is, the smaller photoelastic coefficient, the smaller the amount ofchange in birefringence by external forces. When the photoelasticcoefficient is larger than 2.0×10⁻¹¹ Pa⁻¹, since the opticalcharacteristics are significantly changed due to deformation by theexternal forces, the application to an optical film becomes difficult.It is more preferably 1.0×10⁻¹¹ Pa⁻¹ or smaller.

A thickness of the TPSNB resin film of the first aspect in the presentinvention is not particularly limited but it is preferably onesatisfying the optical characteristics and the physical propertiesdescribed when an average film thickness is 100 μm or smaller. In anoptical film comprising a conventional TPSNB resin, when the averagefilm thickness was 100 μm or smaller, it became very brittle and itsproduction was difficult, and in addition when using it as a protectivefilm for a polarizer, the resulting polarizing plate became a substancewhich was poor in reworkability. It satisfies the opticalcharacteristics and the physical properties described more preferablywhen the average film thickness is 70 μm or smaller and furthermorepreferably when the average film thickness is 50 μm or smaller. When ithas the average film thickness of 50 μm or smaller and satisfies theoptical characteristics and the physical properties described, the costcan be significantly reduced and it is extremely valuable. A lower limitof the average film thickness is not particularly limited but,considering the use as an optical film or a protective film for apolarizer, it is preferred that it satisfies the optical characteristicsand the physical properties described preferably when the average filmthickness is 25 μm or larger and more preferably when the average filmthickness is 20 μm or larger.

And, in the TPSNB resin film of the first aspect in the presentinvention, it is preferred that the difference between the maximumthickness and the minimum thickness in measuring a thickness by a methodaccording to JIS K 7130 is 5 μm or smaller. However, in measuring, endportions, namely, the respective 10% portions of the total length onboth sides of a film extruded from a die, are not measured.

The present inventors have found as a result of an intense study thatwhen there are variations in film thicknesses, particularly variationbetween the film thicknesses of the direction of flow and the directionperpendicular (TD) to flow in extruding the film, tensile elongations atbreak also vary widely. When the difference in film thicknesses is morethan 5 μm, it may become a substance which is industrially poor inreworkability even though an average tensile elongation at break cansatisfy the value.

Though, conventionally, there was not such a TPSNB resin film whichrealized the compatibility between optical characteristics and physicalproperties, the present inventors have found as a result of an intensestudy that it is possible to realize the compatibility between opticalcharacteristics and physical properties by controlling the conditions ofthe TPSNB resin and the rubber polymer in the TPSNB resin film, leadingto the completion of the present invention.

That is, when the TPSNB resin film of the first aspect in the presentinvention was dyed with ruthenium tetraoxide and then it was sliced in athickness of about 0.05 μm and the cross section was observed using atransmission electron microscope, if a sectional structure becomes astate in which the rubber polymer is oriented in a certain direction instring or strip form and arrayed in a matrix of the TPSNB resin, theTPSNB resin film can realized the compatibility between the opticalcharacteristics and physical properties. A schematic view showing anexample of a transmission electron microscope image of the TPSNB resinfilm of the first aspect in the present invention being in such a stateis shown in FIG. 1.

In FIG. 1, a rubber polymer 2 is oriented in a certain direction instring or strip form and arrayed in a matrix comprising TPSNB resin 1.The size of the rubber polymer in string or strip form is notparticularly limited but a size of about 10 nm in width, about severaltens to several hundreds nm in thickness and about 0.4 to 5 μm in lengthis preferred.

Further, an arrow in FIG. 1 indicates the thickness direction of theTPSNB resin film, and optical characteristics such as paralleltransmittance in this direction are significant.

When the TPSNB resin film of the first aspect in the present inventiontakes on such a specific structure, it can realize the compatibilitybetween excellent optical characteristics and excellent physicalproperties. The reason for this is considered to be that since therubber polymers are observed to be dispersed in the form of rod or stripof about several tens to several hundreds nm, i.e., below a wavelengthof visible light, in thickness in the TPSNB resin in viewing the TPSNBresin film of the present invention in the thickness direction, atransparent film can be obtained even when a large amount of the rubberpolymer is blended to a degree that physical properties are adequatelyimproved.

Further, in the TPSNB resin film of the first aspect in the presentinvention, it is more preferred that when the rubber polymer oriented ina certain direction in string or strip form and arrayed in a matrixcomprising the TPSNB resin is observed in detail, the TPSNB resin filmtakes on a structure in which a layer of the TPSNB resin is taken inwithin at least a part of the rubber polymer in string or strip form. Anexample of such a structure is shown in FIG. 1 b.

In FIG. 1 b, the TPSNB resin 1 is recognized further within the rubberpolymer 2 in string or strip form in a matrix comprising the TPSNB resin1. Such a structure is generally referred to as a salami structure. Whenthe TPSNB resin film of the first aspect in the present invention has asalami structure, physical properties and optical performance such asreduction of residual retardation are further enhanced.

The reason for this is considered to be that when a force is applied bypulling the TPSNB resin film of the first aspect in the presentinvention, first, a stress is concentrated on an interface between theTPSNB resin and the rubber polymer, which take on the salami structure,and a force to break the film and a strain during molding, which is acause of the residual retardation, are mitigated.

On the other hand, when a conventional TPSNB resin film described inJapanese Kokai Publication Hei-5-148413 is observed with a transmissionelectron microscope, a structure, in which rubber polymer flocculated atrandom floats in a matrix comprising TPSNB resin, is observed. Aschematic view showing an example being in such a state is shown in FIG.2.

In FIG. 2, various sized flocculates of a rubber polymer 2 are locatedat random in a matrix comprising TPSNB resin 1.

In the TPSNB resin film in such a state, since light is scattered withinthe film, it is considered that adequate optical characteristics cannotbe attained when a large amount of the rubber polymer is blended.

In order to control the conditions of the TPSNB resin and the rubberpolymer in the TPSNB resin film like this to obtain the TPSNB resin filmof the first aspect in the present invention having excellent opticalcharacteristics and physical properties, it is important that aftermixing adequately the TPSNB resin and the rubber polymer, and variousadditives as required to prepare a TPSNB resin composition, meltextrusion is performed under special temperature control and furtherspecial temperature control is also performed on temperature conditionsof the extruded film.

That is, in the case of producing the TPSNB resin film by a meltextrusion process, it is possible to realize the state of the TPSNBresin and the rubber polymer shown in FIG. 1 and to produce the TPSNBresin film of the first aspect in the present invention realizing thecompatibility between optical characteristics and physical properties bysetting a melting temperature of the TPSNB resin composition duringmelting the TPSNB resin composition and sending it to a die at atemperature of a glass transition temperature of the TPSNB resin plus135° C. or lower, and by setting an average residence time from meltingit to sending it to a die at 40 minutes or less.

The TPSNB resin composition containing the rubber polymer is alsodisclosed in Japanese Patent Publication No. 2940014, for example.However, there has not been reported at all an example in which anoptical film is prepared considering a measure, which is essential toperformance as an optical film, to reduce defects such as fish eye on afilm using the TPSNB resin composition containing the rubber polymer. Inorder to reduce the fish eye on a film, it is essential to be filteredwith a resin filter and the like in an extruding step, and particularlyin order to satisfy the performance required for the optical film, highaccuracy of filtering, in which a resin filter with filtering accuracyof 10 μm or smaller is used, is required. When the resin filter withfiltering accuracy of 10 μm or smaller is used, there is no other choicebut to increase a size of the resin filter due to high pressure loss,and therefore an average residence time of resin tends to increase. And,it has been common to mold it at elevated temperature to reduce pressureloss in a filter by decreasing the viscosity of resin so as not to causedeterioration of film performance due to deterioration of a resin,considering an increase in pressure loss by plugging due to continuousoperation. However, the present inventors have found that when the TPSNBresin composition containing the rubber polymer is formed in film formby such a conventional method, cohesion of the contained rubber polymeroccurs and an optical film having the high parallel transmittance andthe small haze cannot be obtained.

If a melting temperature of the TPSNB resin composition is higher than atemperature of a glass transition temperature of the TPSNB resin plus135° C. or an average residence time is larger than 40 minutes, thestate of the TPSNB resin and the rubber polymer shown in FIG. 1 cannotbe realized due to the occurrence of cohesion of the rubber polymer, andthe parallel transmittance and the haze of the TPSNB resin film to beobtained will be deteriorated. A preferable melting temperature is aglass transition temperature of the TPSNB resin plus 130° C. or lower. Apreferable average residence time is 35 minutes or smaller and a morepreferable average residence time is 30 minutes or smaller. Such amethod producing the TPSNB resin film also constitutes the presentinvention.

And, the TPSNB resin composition containing the rubber polymer tends todecrease in melt viscosity compared to a simple TPSNB resin.Accordingly, when the TPSNB resin film is produced using the method ofproducing the TPSNB resin film of the present invention, molding at lowtemperature becomes possible, gelation of the TPSNB resin can beinhibited and a long-duration continuous manufacturing becomes possible.This can be said to be also an effect of using the rubber polymer.Further, the present inventors have found on the gelation of the TPSNBresin that the gelation of the TPSNB resin can be inhibited and fish eyeof the obtained film can be reduced particularly when using, as atemperature for melting, a temperature at which the time that elapsedbefore the glass transition temperature increases by 1° C. is 40 hoursor more in keeping the TPSNB resin at a constant temperature in anatmosphere of nitrogen and measuring its glass transition temperaturewith a differential scanning calorimeter (DSC) every one hour. Bymolding the resin in such a temperature condition, a long-durationcontinuous manufacturing becomes possible.

A method of melt extruding it is not particularly limited and aconventional method publicly known can be used. For example, there isgiven a method in which after it is kneaded with a uniaxial or biaxialscrew, it is melt extruded in film form with a T die, taken off by achill roll and solidified by cooling.

A method of preparing the TPSNB resin composition is not particularlylimited and includes, for example, a method of melt kneading it at atemperature which is higher by 50 to 150° C. than a glass transitiontemperature of the TPSNB resin using, for example, a uniaxial kneader, amixer, a biaxial kneader, and the like; a method of kneading under asupercritical condition; and a method of dissolving it in an appropriatesolvent and then removing the solvent by a coagulation method, a castingmethod or a directly dry method, and the like.

In addition, preparation and film molding of the TPSNB resin compositionmay be performed in a sequential process, or the TPSNB resin compositionmay be processed in pellet form once and then a film is molded usingthis pellet.

In the method of producing a TPSNB resin film of the present invention,a distance between a die outlet and a contact point of a chill roll,namely, an air gap, is preferably 100 mm or less. When the air gap isless than 100 mm or less, it is less affected externally during aprocess and a film having a uniform thickness and uniform opticalperformance can be obtained.

And, in the method of producing a TPSNB resin film of the presentinvention, temperature, immediately prior to contact with the chillroll, of the TPSNB resin composition extruded from a die is preferably aglass transition temperature of the TPSNB resin plus 50° C. or more. Bysetting it at the glass transition temperature of the TPSNB resin plus50° C. or more, a stress generated in molding the TPSNB resin film fromthe TPSNB resin composition is significantly reduced and therefore theoccurrence of residual retardation can be suppressed. The reason forthis is that in the case of amorphous thermoplastic resin such as TPSNBresin, the higher temperature of resin becomes, the less a stress isgenerated in being deformed. It is more preferably a glass transitiontemperature plus 80° C. or more.

Also, it is preferred to keep variations in temperature of the TPSNBresin composition immediately prior to contact with the chill roll lowerthan 10° C. Even when the temperature of the TPSNB resin composition isadjusted to the glass transition temperature plus 50° C. or more asdescribed, in the case of varying in temperature, variations in stressesresulting from deformation of the resin develop, and therefore someresins may vary in residual retardation and displacement of the opticalaxis may also be generated due to the stress concentration on a part.

Further, in the method of producing the TPSNB resin film of the presentinvention, temperature of the TPSNB resin composition immediately afterhaving been extruded from a die is preferably a glass transitiontemperature of the TPSNB resin plus 100° C. or more. When it is lowerthan the glass transition temperature plus 100° C., a stress generatedin molding it may become significantly large and therefore the residualretardation becomes apt to occur.

Thus, a method of controlling the temperature of the TPSNB resincomposition extruded from a die is not particularly limited andincludes, for example, a method of controlling a temperature of a die orpolymer piping (adapter) by using, for example, a temperature controllerwith PID control function. In this case, a temperature of a die orpolymer piping(adapter) is a temperature of a level of not thermallydegrading resin. And, an approach, which keeps a temperature of the filmby heating with a heater or using an thermal insulation cover at the airgap, is also conceivable. This approach can control temperature withhigh accuracy compared with a method of changing a temperature of a dieand decreases variations in temperature, and therefore it isparticularly effective for the case required to control temperature withhigh accuracy. And, since it is not necessary to increase a temperatureof a die excessively, there is a merit of inhibiting degradation inresin.

Further, it is preferred to press the TPSNB resin composition againstthe chill roll at the downstream of a contact point in contacting theTPSNB resin composition melted and extruded with the chill roll.Thereby, the change in temperature of the TPSNB resin compositionbecomes uniform, and therefore displacement of the optical axis can beprevented and a film, which has a stable profile of thickness and auniform thickness, is obtained.

A method of pressing the TPSNB resin composition against the chill rollis not particularly limited and includes, for example, a method such asan air knife, an air chamber, electrostatic pinning, a touch roll. Here,it is more preferable that temperature and pressure in the direction ofwidth are uniform.

Preferably, the chill roll has the surface roughness Ry of 0.5 μm orsmaller. When the surface roughness is larger than 0.5 μm, smoothness ofthe TPSNB resin film cannot be maintained and transparency of the TPSNBresin film may be poor. It is more preferably 0.3 μm or smaller.Incidentally, the surface roughness Ry can be measured by a methodaccording to JIS B 0601. And, material of the chill roll is notparticularly limited and includes, for example, carbon steel, stainlesssteel.

In the method of producing the TPSNB resin film of the presentinvention, it is preferred that a clearance of a die outlet attached toan extruder used is set in advance corresponding to design of a flowpath of a die. An error of the same level as the variations in the filmthickness is acceptable. Further, when the die is equipped with aplurality of clearance adjustment bolts, it may be adjustedcorresponding to the thickness in extruding the film actually.

Since the TPSNB resin film of the first aspect in the present inventionrealizes the compatibility between excellent optical characteristics andphysical properties as described, it can be suitably used as an opticalfilm.

An optical film comprising the TPSNB resin film of the first aspect inthe present invention also constitutes the present invention.

The TPSNB resin film of the first aspect in the present invention canalso be suitably used as a protective film for a polarizer. A protectivefilm for a polarizer comprising the TPSNB resin film of the first aspectin the present invention also constitutes the present invention.

The protective film for a polarizer of the present invention may bevariously surface treated with reference to applications of a liquidcrystal display to be used. The surface treatment is not particularlylimited and includes, for example, clear hard coat treatment, AG(anti-glare) treatment, and AR (anti-reflection) treatment.

For the purpose of enhancing a bonding property to a polarizer, coronadischarge treatment and the like may be applied to the protective filmfor a polarizer of the present invention in such a way a contact angleof water on the surface is about 40 to 500 within the limits of notimpairing optical characteristics.

The TPSNB resin film of the first aspect in the present invention canalso be suitably used as a retardation film which compensates a strainof light in passing through a liquid crystal material by uniaxially orbiaxially drawing to impart orientation. A retardation film comprisingthe TPSNB resin film of the first aspect in the present invention alsoconstitutes the present invention. Further, a polarizing plate, which isobtainable by laminating the retardation film of the present inventiondirectly on at least one side of the polarizer, also constitutes thepresent invention.

A temperature in performing the drawing is not particularly limited butit is preferably within a range of from the glass transition temperatureof the TPSNB resin to the glass transition temperature of the TPSNBresin plus 20° C. When it is out of this range, the resin film may breakon a lower temperature side and desired retardation value may not beattained on an upper temperature side. It is more preferably within arange of from the glass transition temperature of the TPSNB resin plus1° C. to the glass transition temperature of the TPSNB resin plus 10° C.

A draw ratio in performing the drawing is not particularly limited butit is preferably 1.05 to 5.0 in the case of drawing in a direction ofmelt extrusion of a film. When the ratio is less than 1.05, sufficientretardation may not be attained because of too small magnitude ofdeformation, and when it is more than 5.0, a film may break. It is morepreferably 1.1 to 2.5. Also, in the case of drawing in a directionperpendicular to the direction of melt extrusion of a film, it ispreferably 1.2 to 3.0 and more preferably 1.5 to 2.5.

The second aspect in the present invention pertains to a polarizingplate which comprises a protective film for a polarizer, comprising anorbornene resin composition, and a polarizer, parallel transmittancebeing 40% or more, and the polarizing plate not breaking in peeling offit with a tensile speed of 300 mm/min and tension of from 2.5 to 3 N/25mm under the conditions of a 180 degree peel test according to JIS Z1528.

The polarizer is not particularly limited and a conventional onepublicly known can be used, and for example, a substance obtainable byallowing a polyvinyl alcohol resin oriented by drawing to adsorb iodineor dye with dichroism can be used.

The polarizing plate of the second aspect in the present invention doesnot break in peeling off it with a tensile speed of 300 mm/min andtension of from 2.5 to 3 N/25 mm under the conditions of a 180 degreepeel test according to JIS Z 1528.

Generally, a polarizing plate is required to be bonded to a liquidcrystal cell at a strength of the order that the polarizing plate is notpeeled off from the liquid crystal cell due to a stress generated by thethermal shrinkage of the polarizer comprising polyvinyl alcohol and thelike and the dimensional change of the whole polarizing plate issuppressed. The adhesion force required for this is considered to be atleast about 2.5 to 3 N/25 mm as peel strength in measuring at a tensilespeed of 300 mm/min in a 180 degree peel test according to JIS Z 1528.Therefore, the polarizing plate of the second aspect in the presentinvention, having a characteristic of not breaking in peeling off itwith a tensile speed of 300 mm/min and a tension of from 2.5 to 3 N/25mm under the conditions of a 180 degree peel test of JIS Z 1528, has theexcellent reworkability.

In the polarizing plate of the second aspect in the present invention,parallel transmittance is 40% or more. When it is less than 40%, thereoccurs a defective condition that the image displayed becomesinsufficient in brightness and hard to view when it is used as apolarizing plate for a liquid crystal.

In the polarizing plate of the second aspect in the present invention,it is preferred that the rate of change in dimensions measured beforeand after heating at 90° C. for 24 hours is 2% or less. When it is morethan 2%, it becomes necessary to bond them at high strength larger than3N/25 mm in order to prevent the polarizing plate from peeling off fromthe liquid crystal cell due to a stress generated in the change of thedimension, and therefore the reworkability may be poor.

A method of fabricating the polarizing plate of the second aspect in thepresent invention is not particularly limited and includes, for example,a method of bonding, the polarizer and the protective film for apolarizer of the present invention comprising the TPSNB resin film ofthe first aspect in the present invention using a publicly known(pressure sensitive) adhesive such as polyurethane, polyester orpolyacrylic adhesive; and acrylic, siliconic or rubber pressuresensitive adhesive. In addition, on the occasion of bonding, heatbonding may be used in a mild condition of the extent that a polarizingfunction of a polarizer is not deteriorated.

The polarizing plate of the second aspect in the present inventionexhibits extremely excellent optical characteristics and further alsohas the extremely excellent reworkability.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail byway of examples, but the present invention is not limited to theseexamples.

EXAMPLE 1

(1) Preparation of TPSNB Resin Film

TPSNB resin (ARTON G6810 produced by JSR Corporation:

-   -   glass transition temperature 164° C., refractive index 1.52) and        styrenic elastomer (Tuftec H1041 produced by ASAHI KASEI        CORPORATION: refractive index 1.51, content of styrene 32%,        content of ethylene 43%) were supplied to a biaxial melt        extruder in proportions by weight of 90:10, and melted and mixed        at 286° C., and the mixture was pelletized and pre-dried at        110° C. for 3 hours and a TPSNB resin composition was prepared.

The resulting TPSNB resin composition was used and extruded and moldedunder the temperature conditions shown in Table 1 through the followingextruder, T die and resin filter and an optical film having an averagethickness of 40 μm was obtained.extruder: uniaxial extruder with a T die of 90 mm in diameter and L/D=28

-   -   T die: coat hanger type of 1,500 mm in width, the surface of a        resin flow path is plated with H—Cr.    -   resin filter: leaf disk type filter (manufactured by Nippon        Seisen Co., Ltd., filtering accuracy 10 μm)

And, as a contact point stabilizer, there was used an elastic touch rollequipped with a metal sleeve on its surface. Then temperature of theelastic touch roll and a chill roll was set at 70° C. Further, thesurface roughness of the elastic touch roll and the chill roll was 0.2μm in Ry. In addition, temperature of the resin composition immediatelyprior to contact with the chill roll was measured with a non-contactthermometer with the elastic touch roll being separated from the chillroll.

Further, after keeping the used TPSNB resin at 286° C. purged by 99.9%with nitrogen, its glass transition temperature was measured with a DSC(DSC 6200R manufactured by Seiko Instruments Inc.) while flowing anitrogen gas at a rate of 60 mL/min and the time that elapsed before theglass transition temperature increases by 1° C. was determined and itwas 120 hours.

(2) Preparation of Polarizing Plate

A not-yet-drawn film (thickness: 75 μm) of polyvinyl alcohol (degree ofpolymerization: 3,800, degree of saponification: 99.5 mol %) was cleanedwith water of room temperature and then drawn by six times in thelongitudinal direction, and it was immersed into an aqueous solutioncontaining iodine in an amount 0.5% by weight and potassium iodide in anamount 5% by weight while retaining this drawn condition and then,furthermore, crosslinked for 5 minutes in an aqueous solution of 50° C.containing boric acid in an amount 10% by weight and potassium iodide inan amount 10% by weight and a polarizer was prepared.

The obtained TPSNB resin film was used as a protective film for apolarizing plate.

First, corona discharge treatment was applied to the side, which will belaminated with a polarizer, of the surface of the film. A contact angleof water on the surface of the protective film for a polarizing platetreated with corona discharge was 42 to 44°. Next, a mixture of Aagent/B agent=10/3(by weight) of a two component type waterborneurethane adhesive (EL-436 A/B produced by TOYO-MORTON, LTD.) was dilutedwith water in such a way that solid matter is 10% by weight to preparean adhesive solution, and it was applied to the side, treated throughcorona discharge, of the protective film for a polarizing plate with amayer bar No. 8, and this was bonded to both sides of a polarizer and alaminate was obtained.

The resulting laminate was retained for 72 hours in a thermostat of 45°C., and dried and cured and a polarizing plate was fabricated.

EXAMPLE 2

TPSNB resin (ARTON G6810 produced by JSR Corporation) used in Example 1and styrenic elastomer (G1652 produced by KRATON Polymers Group ofCompanies: refractive index 1.52, content of styrene 28%, content ofethylene 45%) were supplied to a biaxial melt extruder in proportions byweight of 85:15, and melted and mixed at 286° C., and the mixture wassent to a T die heated at 286° C. in a residence time of 30 minutes. ATPSNB resin film having a thickness of 30 μm was obtained by the sameprocedure as in Example 1 except for the conditions shown in Table 1. Apolarizing plate was prepared by the same procedure as in Example 1using the obtained TPSNB resin film as a protective film for apolarizing plate.

EXAMPLE 3

TPSNB resin (ARTON G6810 produced by JSR Corporation) used in Example 1and styrenic elastomer (Tuftec 1041 produced by ASAHI KASEICORPORATION), were supplied to a biaxial melt extruder in proportions byweight of 90:10, and melted and mixed at 293° C., and the mixture wassent to a T die heated at 293° C. in a residence time of 30 minutes. ATPSNB resin film having a thickness of 30 μm was obtained by the sameprocedure as in Example 1 except for the conditions shown in Table 1. Apolarizing plate was prepared by the same procedure as in Example 1using the obtained TPSNB resin film as a protective film for apolarizing plate.

Further, after keeping the used TPSNB resin at 293° C. purged by 99.9%with nitrogen, its glass transition temperature was measured with a DSC(DSC 6200R manufactured by Seiko Instruments Inc.) while flowing anitrogen gas at a rate of 60 mL/min and the time that elapsed before theglass transition temperature increases by 1° C. was determined and itwas 40 hours.

EXAMPLE 4

TPSNB resin (ARTON G6810 produced by JSR Corporation) used in Example 1,styrenic elastomer (KRATON RP6936 produced by KRATON Polymers Group ofCompanies: refractive index 1.51, content of styrene 40%) andthermoplastic resin (Escorez 235E produced by Tonex Corporation) weresupplied to a biaxial melt extruder in proportions by weight of80.5:15:4.5, and melted and mixed at 286° C., and the mixture waspelletized and pre-dried at 110° C. for 3 hours and a TPSNB resincomposition was obtained.

The resulting TPSNB resin composition was used and a TPSNB resin filmhaving a thickness of 40 μm was obtained by the same procedure as inExample 1 except for the conditions shown in Table 1. A polarizing platewas prepared by the same procedure as in Example 1 using the obtainedTPSNB resin film as a protective film for a polarizing plate.

EXAMPLE 5

TPSNB resin (ARTON G6810 produced by JSR Corporation) used in Example 1and styrenic elastomer (KRATON RP6936 produced by KRATON Polymers Groupof Companies) were supplied to a biaxial melt extruder in proportions byweight of 85:15, and melted and mixed at 286° C., and the mixture waspelletized and pre-dried at 110° C. for 3 hours and a TPSNB resincomposition was obtained.

The resulting TPSNB resin composition was used and a TPSNB resin filmhaving a thickness of 40 μm was obtained by the same procedure as inExample 1 except for the conditions shown in Table 1. A polarizing platewas prepared by the same procedure as in Example 1 using the obtainedTPSNB resin film as a protective film for a polarizing plate.

EXAMPLE 6

TPSNB resin (ARTON G6810 produced by JSR Corporation) used in Example 1,styrenic elastomer (KRATON RP6936 produced by KRATON Polymers Group ofCompanies: refractive index 1.51, content of styrene 40%) andthermoplastic resin (Escorez 235E produced by Tonex Corporation) weresupplied to a biaxial melt extruder in proportions by weight of 89:10:1,and melted and mixed at 286° C., and the mixture was pelletized andpre-dried at 110° C. for 3 hours and a TPSNB resin composition wasobtained.

The resulting TPSNB resin composition was used and a TPSNB resin filmhaving a thickness of 40 μm was obtained by the same procedure as inExample 1 except for the conditions shown in Table 1. A polarizing platewas prepared by the same procedure as in Example 1 using the obtainedTPSNB resin film as a protective film for a polarizing plate.

COMPARATIVE EXAMPLE 1

Only TPSNB resin (ARTON G6810 produced by JSR Corporation) used inExample was supplied to a uniaxial melt extruder and a TPSNB resin filmhaving a thickness of 30 μm was obtained by the same procedure as inExample 1 except for the conditions shown in Table 1. A polarizing platewas prepared by the same procedure as in Example 1 using the obtainedTPSNB resin film as a protective film for a polarizing plate.

COMPARATIVE EXAMPLE 2

A TPSNB resin film and a polarizing plate were prepared by the sameprocedure as in Example 5 except for changing the residence time in theextruder to 50 minutes.

COMPARATIVE EXAMPLE 3

A TPSNB resin film and a polarizing plate were prepared by the sameprocedure as in Example 5 except for changing the extrusion temperatureto 310° C.

Further, after keeping the used TPSNB resin at 310° C. purged by 99.9%with nitrogen, the glass transition temperature was measured with a DSC(DSC 6200R manufactured by Seiko Instruments Inc.) while flowing anitrogen gas at a rate of 60 mL/min and the time that elapsed before theglass transition temperature increases by 1° C. was determined and itwas 12 hours.

COMPARATIVE EXAMPLE 4

TPSNB resin (ARTON G6810 produced by JSR Corporation) used in Example 1and styrenic elastomer (G1652 produced by KRATON Polymers Group ofCompanies) were dissolved into toluene in proportions by weight of 90:10to prepare a solution, and a TPSNB resin film having a thickness of 40μm was obtained by a casting method using this solution.

The obtained TPSNB resin film became a heterogeneous and opaque film dueto the occurrence of phase separation between the TPSNB resin and thestyrenic elastomer.

A polarizing plate was prepared by the same procedure as in Example 1using the obtained TPSNB resin film as a protective film for apolarizing plate.

With respect to the TPSNB resin films prepared in Examples 1 to 6 andComparative Examples 1 to 4, a tensile elastic modulus, a tensileelongation at break, total transmittance, parallel transmittance, hazevalue, residual retardation, displacement of the optical axis, aphotoelastic coefficient, variations in a film thickness, occurrence offish eye and a rewinding property were measured according to thefollowing method. In addition, the TPSNB resin film prepared in Example1 was observed to evaluate the presence or absence of a salami structureusing a transmission electron microscope according to the followingmethod.

Further, with respect to the polarizing plates prepared in Examples 1 to6 and Comparative Examples 1 to 4, parallel transmittance was measuredand a breaking property in peeling and endurance were evaluatedaccording to the following method.

The results are shown in Tables 2 and 3 and FIG. 3.

(1) Measurement of Tensile Elastic Modulus and Tensile Elongation atBreak of TPSNB Resin Film

Measurement was conducted under the following conditions using TENSILON(manufactured by ORIENTEC Co., Ltd.) according to JIS K 7113. distancebetween chucks 150 mm film width 20 mm tensile speed 20 mm/min(2) Measurement of Total Transmittance, Parallel Transmittance and HazeValue of TPSNB Resin Film

Measurement was conducted using a haze meter (TC-H III DKP manufacturedby Tokyo Denshoku CO., LTD.) according to JIS K 7105.

(3) Measurement of Residual Retardation and Displacement of the OpticalAxis of TPSNB Resin Film

Measurement was conducted at a measurement wavelength of 590 nm using anautomatic birefringence analyzer (KOBRA-21ADH manufactured by OjiScientific Instruments)

(4) Measurement of Photoelastic Coefficient of TPSNB Resin Film

Each film was cut off in a size of 10 mm in width and 100 mm in length,and loads of 0, 500, 1,000 and 1,500 g in a direction of a long sidewere imposed on each film. Under this condition, the retardation wasmeasured at a measurement wavelength of 550 nm using KOBRA-21ADHmanufactured by Oji Scientific Instruments. A photoelastic coefficientwas determined from the slope of an approximate straight line obtainedby plotting the retardation with respect to load.

(5) Measurement of Variations in Thickness of TPSNB Resin Film

A film thickness was measured by a method according to JIS K 7130, andthe difference between the maximum value and the minimum value wasdetermined. Model Millitron 1240 manufactured by Seiko EM was used formeasurement.

(6) Evaluation of Occurrence of Fish Eye

Number of fish eyes of 100 μm square or larger in the obtained film wasvisually observed, and the time, which elapses from the start ofproduction up to the moment when the number of generated fish eyesexceeds 10/m² was measured.

(7) Evaluation of Rewinding Property of TPSNB Resin Film

Each film was subjected to a rewinding test under the conditions of aline speed of 5, 10 and 30 m/min, rewinding tension of 500 N/650 mm anda FRP rewinding core of 6 inch, and the presence or absence offilm-break was evaluated.

(8) Observation of TPSNB Resin Film with Transmission ElectronMicroscope

After the TPSNB resin film was dyed with ruthenium tetraoxide, the filmwas sliced in a thickness of about 0.05 μm in a machine direction (MD)and in a transverse direction (TD) in extrusion molding with amicrotome, and each cross section was observed using a transmissionelectron microscope (JEM-1200EX II manufactured by JEOL LTD.) andphotograph was taken. In addition, the presence or absence of a salamistructure was evaluated based on this photograph.

(9) Measurement of Parallel Transmittance of Polarizing Plate

Measurement was conducted using a haze meter (TC-H III DKP manufacturedby Tokyo Denshoku CO., LTD.) according to JIS K 7105.

(10) Evaluation of Breaking Property in Peeling Polarizing Plate

<Preparation of Pressure Sensitive Adhesive and Non-Support Tape>

94.8 parts by weight of butyl acrylate, 5 parts by weight of acrylicacid, and 0.2 parts by weight of 2-hydroxyethyl methacrylate werecopolymerized in a solvent of ethyl acetate in the presence of 0.3 partsby weight of benzoyl peroxide and an ethyl acetate solution of acrylicpolymer having a weight average molecular weight (Mw) of 1,200,000 andmolecular weight distribution of 3.9 was obtained.

Toluene was added to the obtained ethyl acetate solution of acrylicpolymer and the solution was diluted, and 13% by weight toluene solutionof acrylic polymer was prepared. And, 2 parts by weight of an isocyanatecrosslinking agent (CORONATE L produced by NIPPON POLYURETHANE INDUSTRYCO., LTD.) was added and the mixture was stirred and a pressuresensitive adhesive was prepared.

The obtained pressure sensitive adhesive was applied onto a release filmand dried in two stages of 60° C. for 5 minutes and 120° C. for 5minutes so as not to foam, and then a release film of an easy releasetype was further laminated on and temporarily attached to the surface ofthe pressure sensitive adhesive and a non-support tape having athickness (average value) after dried of 25 μm was fabricated.

<Fabrication of Test Piece>

The release film on the easy release side of the non-support tape waspeeled off and it was laminated on the one side of a polarizing plateand a pressure sensitive adhesive sheet of polarizing plate wasfabricated. The obtained pressure sensitive adhesive sheet of polarizingplate was cut off in the form of a rectangle of 25 mm×150 mm in such away that an angle of a polarizer absorption axis is 0 degrees and 90degrees relative to a long side. Next, the release film on thenon-support tape was peeled off and it was bonded to nonalkaline glassof 1.1 mm in thickness with a 2 kg roller. Further, this was autoclavedin the conditions of 50° C. and 5 atoms and a test piece was prepared.

<Peeling Test>

With respect to each of the obtained test piece in which an angle of apolarizer absorption axis is 0 degrees relative to a long side and testpiece in which an angle of a polarizer absorption axis is 90 degreesrelative to a long side, a state of the polarizing plate in peeling offit with a tensile speed of 300 mm/min under the conditions of a 180degree peel test according to JIS Z 1528 using TENSILON (manufactured byORIENTEC Co., Ltd.) was visually observed and evaluated according thefollowing criteria. Incidentally, the peeling force in the test wasabout 3 N/25 mm.

-   -   ◯: it was peeled off from the glass plate completely without        breaking.    -   x: it broke during peeling and part of it was remained on the        glass plate.        (11) Evaluation of Endurance of Polarizing Plate        <Preparation of Pressure Sensitive Adhesive and Non-Support        Tape>

A pressure sensitive adhesive and a non-support tape were prepared bythe same procedure as in the case of the evaluation of breaking propertyin peeling a polarizing plate.

<Fabrication of Test Piece>

The release film on the easy release side of the non-support tape waspeeled off and it was laminated on the one side of the obtainedpolarizing plate, a pressure sensitive adhesive sheet of polarizingplate was fabricated. The obtained pressure sensitive adhesive sheet ofpolarizing plate was cut off in a size of 200 mm×300 mm with an angle ofa polarizer absorption axis being 0 degrees relative to a long side.Next, the release film on the non-support tape was peeled off and it wasbonded to nonalkaline glass of 1.1 mm in thickness at a pressure of 19.6N/25 mm using a roller.

The polarizing plate bonded to the glass was stored for 3 days in anoven of 100° C. and further left standing for 1 week under theconditions of 25° C. in temperature and 50% RH in humidity in athermo-hygrostat, and then the surface of the polarizing plate wasvisually observed and evaluated according to the following criteria.

◯: there is no crack or contaminant and transparency is excellent

-   -   Δ: there are cracks and the polarizing plate is slightly whitish    -   x: transparency is excellent but there are cracks    -   xx: there are significant cracks and the polarizing plate is        whitish

Table 1 Condition of extrusion Resin temperature Extrusion Resintemperature immediately prior to temperature Residence immediately afterAir gap contacting with chill (° C.) time (min) extruding (° C.) (mm)roll (° C.) Example1 286 30 286 90 215 Example2 286 30 286 90 215Example3 293 30 293 90 215 Example4 286 30 286 70 230 Example5 286 30286 70 230 Example6 286 30 286 50 260 Comparative 310 50 310 90 235Example1 Comparative 286 50 286 70 230 Example2 Comparative 310 30 31070 240 Example3 Comparative — — — — — Example4

Table 2 Evaluation of thermoplastic saturated norbornene resin filmTensile Tensile elastic elongation Parallel Haze Residual DisplacementPhotoelastic modulus at break transmittance value retardation of opticalaxis coefficient (MPa) (%) (%) (%) (nm) (

) (×10⁻¹¹Pa⁻¹) Example1 1690 12 91 0.9 3.80 ±8 0.47 Example2 1560 25 911.0 3.70 ±7 0.49 Example3 1710 12 92 0.7 3.20 ±8 0.48 Example4 2030 1491 0.3 2.53 ±8 0.45 Example5 2040 14 92 0.3 2.60 ±8 0.45 Example6 206012 91 0.2 0.80 ±8 0.43 Comparative 2100 2 92 0.1 8.90 ±5 0.40 Example1Comparative 1660 10 80 2.9 3.80 ±8 0.47 Example2 Comparative 1650 10 813.5 0.80 ±20 0.47 Example3 Comparative 1500 8 70 15.2 — — — Example4Evaluation of thermoplastic saturated norbornene resin film Presence orRewinding property Variations Occurrence absence of (presence or absenceof break) in thickness of fish eye salami 5 m/min 10 m/min 30 m/min (μm)(hour) structure Example1 none none none 5 110 present Example2 nonenone none 8 110 present Example3 none none none 7 43 present Example4none none none 4 110 present Example5 none none none 5 110 presentExample6 none none none 4 110 present Comparative present presentpresent 5 11 none Example1 Comparative none none none 8 95 none Example2Comparative none none none 8 12 none Example3 Comparative — — — 5 — noneExample4

Evaluation of polarizing sheet Parallel Breaking property in peelingtransmittance Endurance Test piece Test piece (%) test of 0 degrees of90 degrees Example1 42 ∘ ∘ ∘ Example2 41 ∘ ∘ ∘ Example3 42 ∘ ∘ ∘Example4 42 ∘ ∘ ∘ Example5 42 ∘ ∘ ∘ Example6 42 ∘ ∘ ∘ Comparative 42 x xx Example1 Comparative 38 Δ ∘ ∘ Example2 Comparative 38 Δ ∘ ∘ Example3Comparative 35 xx x x Example4

EXAMPLE 9

Using the TPSNB resin film prepared in Example 1, a retardation film wasfabricated. Nip rollers were equipped on both sides of outside of aheating furnace divided into three zones, that is, preheating zone,drawing zone and cooling zone, in the longitudinal direction, and it wascontinuously wound off at a constant speed of 5.0 m/min from the inletnip roller, while being drawn at a speed of 7.5 m/min at the outlet niproller in such a way that a draw ratio is 150%. Temperature setting was153° C. at the preheating zone, 166° C. at the drawing zone and 120° C.at the cooling zone and a uniaxial retardation film was obtained.

With respect to the obtained retardation film, retardation in inputtinglight with a wavelength of 589 nm was measured using an automaticbirefringence analyzer (KOBRA-21ADH manufactured by Oji ScientificInstruments) and it was 160 nm.

INDUSTRIAL APPLICABILITY

In accordance with the present invention, it is possible to provide thethermoplastic saturated norbornene resin film, the optical film, theprotective film for a polarizer, the retardation film, the polarizingplate and the method of producing the thermoplastic saturated norborneneresin film, which realize the compatibility between excellent physicalproperties and optical characteristics.

1. A thermoplastic saturated norbornene resin film, which is obtainableby using a thermoplastic saturated norbornene resin compositioncontaining a thermoplastic saturated norbornene resin in an amount of100 parts by weight and a rubber polymer in an amount of 5 to 40 partsby weight, parallel transmittance being 87% or more.
 2. Thethermoplastic saturated norbornene resin film according to claim 1,wherein the difference of refractive indexes between the thermoplasticsaturated norbornene resin and the rubber polymer is 0.2 or less.
 3. Thethermoplastic saturated norbornene resin film according to claim 1,which has a tensile elastic modulus of 900 MPa or higher and a tensileelongation at break of 4 to 40%.
 4. The thermoplastic saturatednorbornene resin film according to claim 1, wherein residual retardationis 3 nm or lower and displacement of an optical axis is ±10° or smallerwith respect to a machine direction.
 5. The thermoplastic saturatednorbornene resin film according to claim 1, wherein residual retardationis 1 nm or lower.
 6. The thermoplastic saturated norbornene resin filmaccording to claim 1, wherein the difference between the maximumthickness and the minimum thickness in measuring a thickness by a methodaccording to JIS K 7130 is 5 μm or smaller.
 7. The thermoplasticsaturated norbornene resin film according to claim 1, which may berewinded without breaking with tension of 500 N/650 mm.
 8. Thethermoplastic saturated norbornene resin film according to claim 1,wherein the rubber polymer is a styrenic elastomer.
 9. The thermoplasticsaturated norbornene resin film according to claim 8, wherein thestyrenic elastomer is a styrene-ethylene-butylene copolymer, the contentof a styrene component being 25 to 50% by weight and the content of anethylene component being 25 to 50% by weight.
 10. The thermoplasticsaturated norbornene resin film according to claim 1, wherein thethermoplastic saturated norbornene resin composition further contains athermoplastic resin having a number average molecular weight of 300 to10,000.
 11. The thermoplastic saturated norbornene resin film accordingto claim 1, wherein a photoelastic coefficient is 2.0×10⁻¹¹ Pa⁻¹ orsmaller.
 12. An optical film, which comprises the thermoplasticsaturated norbornene resin film according to claim
 1. 13. A protectivefilm for a polarizer, which comprises the thermoplastic saturatednorbornene resin film according to claim
 1. 14. A retardation film,which comprises the thermoplastic saturated norbornene resin filmaccording to claim
 1. 15. A polarizing plate, which comprises aprotective film for a polarizer, comprising a norbornene resincomposition, and a polarizer, parallel transmittance being 40% or more,and the polarizing plate not breaking in peeling off the polarizingplate with a tensile speed of 300 mm/min and tension of 2.5 to 3 N/25 mmunder the conditions of a 180 degree peel test according to JIS Z 1528.16. The polarizing plate according to claim 15, wherein a rate of changein dimensions measured before and after heating at 90° C. for 24 hoursis 2% or less.
 17. A polarizing plate, which is obtainable by laminatingthe retardation film according to claim 14 directly on at least one sideof a polarizer.
 18. A method of producing the thermoplastic saturatednorbornene resin film according to claim 1, by a melt extrusion process,wherein a melting temperature of the thermoplastic saturated norborneneresin composition during melting the thermoplastic saturated norborneneresin composition and sending the thermoplastic saturated norborneneresin composition to a die is a glass transition temperature of thethermoplastic saturated norbornene resin plus 135° C. or lower and anaverage residence time from melting the thermoplastic saturatednorbornene resin composition to sending the thermoplastic saturatednorbornene resin composition to a die is 40 minutes or less.
 19. Themethod of producing a thermoplastic saturated norbornene resin filmaccording to claim 18, wherein temperature, immediately prior to contactwith a chill roll, of the thermoplastic saturated norbornene resincomposition extruded from a die is a glass transition temperature of thethermoplastic saturated norbornene resin plus 50° C. or more.
 20. Themethod of producing a thermoplastic saturated norbornene resin filmaccording to claim 18, wherein temperature, immediately prior to contactwith a chill roll, of the thermoplastic saturated norbornene resincomposition extruded from a die is a glass transition temperature of thethermoplastic saturated norbornene resin plus 80° C. or more.